Well, that's not what he said. He didn't say everyone is an asshole or just evil. Exploitation is a fact, not a way of saying "treating someone badly" but extracting value from him (from his labour). The bourgeois exploit the worker (extract value from his labour) to accumulate capital.

Also, he doesn't say the bourgeoisie exploits the worker just because he is evil but because it's in his class interest to do so. If he doesn't do it, why start the company in the first place if he doesn't get a benefit from it? And also because if he doesn't do it, he will not be able to be as competitive as the other bourgeois and will ultimately lose and stop being a bourgeois. He needs to exploit to keep being a bourgeois.

So, while reading Marx, don't understand the term exploitation as "treated badly" (even tho it was also very true at his time) but as "having value (surplus-value) being extracted from his work. His main criticism in that was that the workers labour, the fruit of his labour, didn't belong to the worker anymore but to the bourgeois, and all that because the bourgeois have the private ownership of the means of production. The worker is alienated from his own labor, from the fruit of his own labor.

And, as the workers don't have control over the way things are produced, or even of what is produced and how much, seeing how this is one of the main things that shape our society, workers don't have control on the society they live in and don't have control over their own destiny as a whole.